Manufacture of sodium nitrate



Patented Nov. 25, 1924.

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I. F l E o l ELIAS ANTI-ION CAPPELEN SMITH, OF NEW YORK, N. Y., ASSIGNORTO GUGGEN- HEIM BROTHERS, A GOPARTNERSHIP OE NEW YORK, N. Y.

MANUFACTURE OF SODIUM NITRATE.

N'o Drawing.

To all whom it may concern:

Be it known that I, ELIAS ANrHoN CAP- IELEN SMITH, a citizen of theUnited States of America, residing at New York city, in the county ofNew York, State of New York, have invented certain new and usefulImprovements in Manufacture of Sodium N itrate; and I do hereby declarethe following to be a full, clear, andexact description of theinvention, such as will enable others skilled in the art to which itappertains to make and use the same.

This invention relates to im 'irovemeuts in the extraction and recoveryof nitrate from caliche, and involves improvements which are not onlyparticularly adapted to installations of small or moderate capacity, butalso to installations of the largest magnitude.

The invention also includes a new and improved sodium nitrate producthaving new and improved properties which make it particularly suitablefor use in the chemical and other industries.

In its preferred and complete form, the process of the inventionincludes a cyclic process in which the nitrate is extracted from calicheby cold or tepid leaching, and in which the nitrates are recovered fromthe solution in the form of the new nitrate product by refrigeration, aswell as a process in which the refrigeration of the strong solutioncontaining the nitrate is in part accomplished by heat interchange withthe cold mother liquor which is thereby warmed before its return forfurther use in the leaching operation.

The method of extraction of nitrates from caliche, which is at presentalmost universally used, consists in boiling the caliche together withthe mother liquors from former crystallizations so as to obtaina strongsolution or caldo, and the subsequent cooling of suclfcaldo and thedepositing out of its dissolved nitrate during a period of five or sixdays. This process is attended withheavy incidental losses, such as thesacrifice of about 33% of the total nitrate present in the calichetreated, while a considerable portion of the caliche is at presentrejected on accoupt of its fine state of divislon.

The present invention largely overcomes or avo ds he difliculties and.objections of Application filed January 19, 1922. Serial No. 530,437.

such prior methods of extraction. traction of the nitrate from thecaliche by boiling is wholly dispensed with, together with thesubsequent slow cooling for a long period of time, While the heavyincidental losses in unextracted nitrate and in the fines are largelyavoided. The fines, which are regarded as extremely diflicult oftreatment in the present methods, are made fully available in thepractice of the present invention. By the expression fines is to beunderstood not only the fine material resulting at any step o' theprocess by disintegration of the caliche under treatment, as, forinstance, the fine material which in the present practice passes throughand gathers under the false bottom of the boiling tank, but also all ofthat portion of the caliche broken on the pampa which is at presentrejected on account of its fine state of division.

In carrying out the cyclic process the caliche, crushed to a sizeappropriate to the method of leaching adopted, will be exposed, togetherwith its fines, to the dissolving action of mother liquor of suitablecomposition returned from the crystallization process or of a solutionof suitable concentration whose nitrate content is intermediate betweenthat of the mother liquor and that of the solution suitable for recoverytreatment. This dissolving or extraction is carried out in such a mannerand in such forms of apparatus (appropriate to the method of leachingadopted) and with a leaching solution of such a composition as to bringthe available nitrate in the caliche into substantially completesolution. This extraction or leaching of the caliche is carried out atatmospheric or tepid temperatures. for best results, contain sufficientamounts of protective agents of the character described in the priorapplication of Charles L. Burdick, Serial No. 513,335, filed November 7,1921.

The caliche under treatment, after it has been subjectedto extractionfor the removal of the nitrate, will be subjected to a sulficient numberof wash waters, of graded nitrate strength to remove and displace to agreat extent the stronger solution produced in the leaching operation.With this leaching procedure and with rational applica The ex-.

The leaching solution, should,

tion of wash Waters of suitable character an extraction of at least 90%of theavailable nitrate is readily obtained and the extraction may be ashigh as 95%.

It will be understood that, contrary to the usual practice, all of thecaliche material broken on the pampas may be charged into the leachingapparatus, thus increasing by a large fraction the amount of calichecommonly treated, inasmuch as the invention permits full use to be madeof the fines which have heretofore, in many cases, been entirelyneglected. Moreover, inasmuch as extremely high recovery of nitrate fromcaliche-is realized by the present invention, it will be economicallyprofitable to work a much lower grade of caliche than is feasible in theprevailing practice. For example, in some instances, the so-calledover-burden itself (that is to say, the outer stratum of materialoverlying the caliche and which is usually rejected) may be rich enoughin nitrate to warrant treatment along with the caliche proper, thusgreatly diminishing the cost of the mining operation.

The enriched liquors withdrawn from the leaching apparatus are sent tothe nitrate recovery plant where a portion of their content of nitrateis removed by crystallization, thereby forming a fresh quantity ofmother liquor or treatment solution. This crystallization of the nitratefrom the saturated or nearly saturated solution received from theleaching plant is brought about by cooling the solution by refrigerationto a lower temperature than that of the cold or tepid leaching. If thesolution is .not of proper composition, the nitrate may be admixed withsulfate. In order to avoid the con tamination of the nitrate withsulfate, the solution, which is subjected to refrigeration should be onewhich contains or which has added thereto a sufiicient amount ofprotective a ents of the character referred to in the s 1d applicationof Charles L. Burdick, Serial No. 513,335. When the solution is ofsuitable composition and is subjected to rapid refrigeration withagitation, the nitrate is separated in the form of the new nitrateproduct, hereinafter more fully described. In order for the recoveryplant to operate to best advantage, it should not only refrigerate thecool 'or tepid saturated or. nearly saturated solutions, in order toinduce crystallization, but it must also supply such additionalrefrigeration as is necessary to balance the heat of crystallization ofthe sodium nitrate crystals.

The cyclic rocess is also carried out with circulation o the saturatedor nearly saturated solutions into heat interchan ing relation with thecold mother liquor cm the crystallization plant. By using heatinterchangers, the mother liquor returning from,

the crystallizatibn tanks to the leaching tanks will be warmed, and therefrigeration stored in the refrigerated weak mother refrigerator tanks.

The mother liquor will thus emerge from the heat interchangers at asomewhat lower temperature than atmospheric. This mother liquor can beused to advantage as the cool- 'ing medium in the condenser for therefrigerant (i. e., the ammonia vapors) in which cooling medium the heatof condensation of the vapors of the refrigerant will in turn heat themother liquor so that it will have a certain quantity of surplus heatstored in it when it returns to the leaching tanks; or, where the motherliquor is circulated through a series of tanks, it may be warmed betweensuccessive tanks, or before entering the last leaching tank, thusraising its temperature during or toward the end of the leachingoperation, and increasing the strength of the final strong solution. Themother liquor may also be heated from some other source of waste heatand a certain quantity of surplus heat stored in it. t The amount ofsurplus heat will preferably be suflicient or more than enough tosatisfy 105 the heat necessarily absorbed in dissolving the nitrate fromthe caliche. In the refrigerators and interchangers themselves, therefrigeration applied or recovered must similarly compensate for thisabsorbed heat, in order to bring about the crystallization of thenitrate.

The sequence of operation is shown in the following flow sheet:

Tepid mother liquor-) Iieaching apparatus (Caliche.

Advance and make-up.

Strong solu- Extracted G raded wash 6 tion. caliche. waters [01- 1 Ilowed by Waste heat recovery. Cooling and condensation apparatus.

Mother liquor. Nitrate.

As illustrated in the flow sheet, the strong solution received from theleaching. apparatus enters the heat interchangers at a temperature, forexample, of 25 C. The heat interchangers may be of any appropriate type,but preferably they are of such construction as. to present a largesurface of contact and a prolonged contact surface between the solutionspassing therethrough in counter current flow. In these heatinterchangers the strong solutions are cooled by the counter flowagainst colder mother liquor returning from the refrigeration tanks. Thetemperature of the strong solution may, for example, be reduced in theheat interchange system, from 25 C. to about 6 C., so that aconsiderable part of the nitrate will be precipitated and recovered inthe tanks of the heat interchanging system in a substantially pure form.

In the refrigerator proper the temperature will be further lowered, forexample, to about 0 (3., and a further quantity of nitrate will beprecipitated. It will, of course, be understood that, in its passagethrough the heat interchangers and the refrigerator, the solution losesbut part of its nitrate and a large part still remains .dissolved in themother liquor and returns again to re-enter the solution cycle. Thenitrate precipitated in the heat interchang ers and the refrigerator maybe discharged therefrom automatically and continuously by any suitablemechanical arrangements. The refrigerator may be provided with anysuitable means of refrigeration, as, for instance, by means of ammoniavaporization or cold brine solution. The system of heat interchangersand refrigerators, together with the intermediate connections, may beinsulated to eliminate atmospheric influences. Different forms of heatinter changers and refrigerating'devices are well known and need not bespecifically described, for example, liquid ammonia may be vaporized atlow pressure, in the usual manner, in the refrigerator coils, and thencompressed and condensed in the customary manner incident to ammoniacooling processes, and, as above described, the heat of compression andcondensation may be utilized in heating the mother liquors to assist inthe leaching operation.

The mother liquor from the refrigerators is. preferably returned bycounterflow through the heat interchangers where it is warmedto, say 20,more or less. The stored refrigeration in the mother liquor is thussimultaneously transmitted to the fresh incoming strong solution. Fromthe heat interchangers, or, in certain cases from the refrigeratorsthemselves, the mother liquor passes through the ammonia condenser(which, for example, may be of the shell and tube type) or through otherforms of waste heat recovery apparatus where it while at-the same timeit is itself raised to a' temperature intermediate between its entrancetemperature and the temperature of the condensing refrigerant, so thatit returns to the leaching tanks at a correspondingly increasedtemperature.

In the extraction of caliche with Water not only does the nitratedissolve, but all the other soluble constituents pass into solution. Itis not objectionable for these salts to build up in the solutionsprovided they do not contaminate the nitrate product obtained from therefrigerating process. The chief impurity which is encountered in thesolutions is sodium chloride, together with lesser amounts of sulfates,potassium salts, borates, iodates, and magnesium. For example, theconcentrations of the major foreign salts dissolved in a mother liquorproduced in the operation of the refrigeration process, were found, inone instance, to be a total of 200 grams per liter of chlorine expressedas sodium chloride, and a total of grams per liter of sulfate expressedas sodium sulfate.

The sodium chloride (which occurs in the caliche in large quantities)does not interfere in the operation of the refrigerating cycle, inasmuchas its solubility (in the presence of sodium nitrate) increases as thetemperature decreases, so that there is no tendency for it toprecipitate along with the nitrate.

Sodium sulfate, however, (which also may occur in considerablequantities in the caliche) presents solubility relations somewhatsimilar to those of the nitrate, in that, below a certain point, (whichin the normal solution encountered is in the neighborhood of 8 itssolubility decreases as the temperature is lowered. The concentrationsof sodium sulfate encountered in the solutions are, however, such thatdown to a temperature of at least 4 Chthere is no substantial danger ofprecipitation, particularly if protective agents are present in theproper amount. Consequently, the sodium nitrate crystals contained inthe heat interchanger are practically free from precipitated sulfate.

In the refrigerators, a further precipitation of the sodium nitratecrystals will occur, and, at the same time, there may be precipitated,at the lower temperatures, a quantity of sodium sulfate, which maythereafter he removed by processes understood in the art. However, inthe preferred practice of the invention, with the production ofsolution, in the leaching, of concentrations suflicientlyhigh innitrate, and with stabilizing agents, such as salts of magnesium andpotassium, borates and iodates,

quantity of sodium sulfate in solution (i. e.,

the quantity of sodium sulfate as distinguished from the total sulfatein solution), the concentration of sulfate in the solutions may bemaintained below such a value that refrigeration at or below 0 C. can beaccomplished with the production of the new nitrate product of acommercially pure and marketable form. Consequently, in accordance withthis additional feature of the invention, by proper regulation oftemperature, and composition of the solution, the new productsubstantially free from sulfate can also be obtained in therefrigerators. This feature of the invention is of particular advantage,inasmuch as it avoids the necessity that would otherwise exist ofsubsequent purification of the nitrate crystals from accompanyingprecipitated sulfate, and insures in a simple and economical way theobtaining of a new nitrate product substantially devoid ofcontaminations, and having new and valuable properties from therefrigerators, in the orderly and regular functioning of the system.

The sodium nitrate produced in the manner above described, byrefrigeration of a nitrate solution of suitable composition, is-

a new and valuable form of sodium nitrate and forms a new nitrateproduct. The new product is in the form of firm, hard, regular facedrhombohedra, especially free from imperfectly developed crystal faces,and of improved appearance, being of a fine uni-- form white appearance.The new nitrate product, obtainable by refrigeration in the manner abovedescribed,

is of an evenly graded character and of a degree of fineness which makesit particularly suitable for use in the chemical industry. In size, theparticles are practically all above 100 mesh and with an average size ofthe crystals of approximately mesh, the particles practically all beingbetween the sizes of 35 mesh (0.4 mm.) and mesh (0.2 mm), so thatapproximatelyall of the product will pass through a 35 mesh screen andwill remain on a 100 mesh screen. The product is, inthis respect,distinguished from the nitrate product commonly produced from the usualboiling process of extracting calichc, which product is much coarser,the particles ranging around 2 to 6 mm. in size, while thefurthercrushing of this material results in a product with aconsiderable amount of very fine material, as well as particles whichare irregular in size and which are lacking in uniformity.

The new product, being made up of small uniform crystals, can be readilydissolved, and completely utilized, while it promotes the regularity andsteadiness of the progress of chemical reactions in which it is used,thus further distinguishing it from the un crushed or crushed productproduced by the usual boiling process of extracting the nitrate fromcaliche.

The new product is also of superior appearance, being of a fine uniformwhite appearance, and it does not set on standing in the same manner asnitrate produced by the present boiling method of extraction. Theseproperties make the product particularly suitable for chemical mixturesand compositions in which the nitrate is introduced as such. Suchmixtures are less apt to become non-uniform through segregation of thenitrate, and also less liable to deteriorate through the absorption ofmoisture.

An important characteristic and advantage of the new product is itsimproved hydroscopic properties.\ The new product' shows considerablyless tendencies to attract moisture from the atmosphere than theordinary nitrate products. Investigations made under equal conditionswith the new product and with the ordinary commercial product (producedby the boiling process of extracting nitrate from caliche) showed thefollowing pronounced difierences and advantages in favor of the newproduct. Like portions of these two materials were exposed toatmospheres of varying humidities at ordinary tempera? tures with thefollowing results :On one days exposure to an atmosphere of 60%humidity, the old nitrate product absorbed 110% more moisture than didthe new product under the same conditions.

sorbed a total of 49% more moisture than did the new product. Onexposure to an atmosphere of 90% humidity, for one day,

the old nitrate product absorbed 82% more moisture, and on exposure forsixteen days it absorbed a total of 19% more moisture,

On sixteen days exposure the old nitrate ab character, the new productof the present invention can be more readily kept in storage, and, undernormal conditions of storage, it is unnecessary to break up or crush theproduct to anywhere .near the same extent that is found to be necessarywith theordinary nitrate products produce in the usual way. Furthermore,the new product is able to carry a higher moisture content without itsphysical properties being affected in any objectionable way. The newproduct is therefore particularly valu able as a component of mixedfertilizers, in which, owing to its improved hydroscopic and otherproperties, it forms a superior ingredient.

The new product is almost completely free from potassium, the. potassiumcontent ranging only from about 0.5% to 0.7%, whereas the ordinarynitrate product ranges from over 2 or 3% up to 25% or more. This freedomfrom potassium is an important advantage in many branches of chemicalindustry where nitrate is used, for example, in nitric acid manufactureand in the manufacture of certain kinds of explosives which containsodium nitrate.

Another characteristic property and ad'- vantage of the new product isits freedom from salts of perchloric acid, the perchlorates beingpresent in only nominal quantities, averaging less than 0.1%perchlorate, figured as sodium perchlorate. This practically completefreedom from perchlorates is an important advantage of the new productin its application in certain industries, in particular, in itsutilization for nitration and the manufacture of certain explosives. Inthe ordinary commercial nitrates the content of perchlorates may be ashigh as 2%, depending upon .the method of production of the nitrate.

It will thus be seen that the new product, obtainable in the mannerabove described, possesses various features which distinguish it andwhich make it advantageous for use in the industries. It is a uniformproduct with particles of substantially uniform size r between about 35mesh and 100 mesh. In

appearance it is a fine white product with uniform regular crystals,giving a sparkling appearance in a beam of sunlight or of directedartificial light. The product is readily distinguishable from theordinary nitrate product by the smaller and uniform size of crystals,and from pulverized nitrate in which the particles are irregular anduneven in character. The new product also possesses improved hydroscopicproperties, absorbing moisture at a rate of from 20 to 25% less thanordinary nitrate under the same conditions of humidity, thus making thenew product more valuable where its hydroscopic properties are ofimportance. The new product is also characterized by an averagepotassium content in the neighborhood of 0.5 to 0.7%, which content doesnot in general exceed about 1%; while it is also practically free fromperchlorates, the con-' tent of which is not inexcess of about 0.1%.

It will thus be seen that the present invention providesboth a newcyclic process of leaching nitrate from caliche, and a new nitrateproduct. The cyclic process includes leaching of the caliche atatmospheric or tepid temperatures and the crystallization of the newnitrate product from the resulting solution by refrigeration andresulting rapid cooling, while agitating the solution and maintaining itof proper composition to prevent contamination of the new nitrateproduct with sulfate or other impurities. The leaching, as hereinbeforestated, may be carried out without extraneous heat, that is to say, ator about ordinary atmospheric temperatures, or the leached liquor may beheated before or during the leaching operation, particularly where asource of waste heat is available. In any event, however, the surplusheat, if any, thus imparted to the leached solutions need not exceed theamount required to maintain the solutions at working temperatures up tobut not substantially higher than about 60 (3., which includes the rangeof temperatures herein referred to as tepid.

I claim:

1. The cyclic method of extracting sodium nitrate from caliche byleaching the caliche at temperatures not exeeding about 60 C. andsubjecting the resulting strong solution to refrigeration for theprecipitation of sodium nitrate therefrom and returning the cold motherliquor for further leaching, which comprises providing and maintainingin the solution during refrigeration a suflicient amount of stabilizingagents to avoid I any substantial precipitation of sulfate when thesolution is cooled to a relatively low temperature, and efi'ecting aheat exchange between the strong solution on its way to therefrigerating step and the cold mother liquor on its return from therefrigerating step to the leaching step.

2. The cyclic method of extracting sodium nitrate from caliche byleaching the caliche at temperatures not exceeding about 60 C.

low temperature, effecting a heat exchange between the strong solutionon its way to the refrigerating stepand the cold mother liquor on itsreturn from the refrigerating step to the leaching step, and furtherut1lizing the cold mother liquor on its way from the refrigerating stepto the leaching step for the condensation of the refrigerant emplayed inthe refrigerating step.

3. The cyclic method of extracting sodium nitrate from caliche byleaching the caliche at temperatures not exceeding about 60 C. and su torefrigeration for the precipitation of sodium nitrate therefrom andreturning the coldmother liquor for further leaching, which comprisescarrying out the refrigeration in successive stages, one of which stagesjecting the resulting strong solution involves a heat exchange betweenthe strong solution from the leaching step and the cold mother liquor inthe course of which sodium nitrate is precipitated, from the strongsolotion, and another of which stages involves refrigeration of thesolution at a lower temperature with a resulting precipitation of sodiumnitrate and the production of said cold mother liquor.

4. The cyclic method of extracting sodium nitrate from caliche byleaching the caliche at temperatures not exceeding about 60 C. andsubjecting the resulting strong solution to refrigeration for theprecipitation of sodium nitrate therefrom and returning the cold motherliquor for further leaching, which comprises providin and maintaining inthe solution during refrigeration a sufiicient amount of stabilizingagents to avoid any substantial precipitation of sulfate when thesolution is cooled to a relatively low temperature, and carrying out therefrigeration in successive stages, one of which stages involves a heatexchange between the strong solution from the leaching step and the coldmother liquor in the course of which sodium nitrate is precipitated fromthe strong solution, and another of which stages involves refrigerationof the solution at a lower temperature with a resulting precipitation ofsodium nitrate and the production of said cold mother liquor.

5. A new sodium nitrate product in the form of firm, hard, regularcrystals of practically uniform size between about 35 and 100 mesh, saidproduct having an average potassium content in'the neighborhood of 0.5to 0.7%, and which content does not in general exceed about 1%, and saidproduct containing an average perchlorate content not in excess of about0.1%, said product being further characterized by improved hydroscopicproperties, being relatively nonhydroscopic in character.

In testimony whereof I afiix my signature.

' ELIAS ANTHON CAPPELEN SNllTl-l.

